There are many instances where it is important that the level of liquid be known with relative accuracy. Thus, the level of lakes, rivers and reservoirs must often be known so that various water control programs can be operated effectively, such as for flood control, irrigation and hydroelectric power generation. It is also important to know the water level in water storage towers as well as the liquid level tanks used for storing oil and other organic liquids, such as gasoline, kerosine, alcohol, chlorine and the like. Turbulent liquids, or liquids with low boiling temperatures, such as liquified natural gas, cause particular gauging problems because of their unsteady surface.
One way in which the liquid level is presently determined is by the use of a float on the liquid. The float is connected to a measuring wire or tape which is then fed to a suitable gauge head where the height of the liquid level is read off directly by observing markings on the tape or wire. Such a measuring system provides an accurate reading for a liquid level only when the liquid level is free of waves or turbulent conditions. This is true even in those instances where vertical movement of the float is guided by wires or rods which extend upright into and above the liquid level to thus prevent the float from being displaced laterally by wave, wind or turbulent action.
Other devices are sometimes used in place of a float to determine the location of the liquid level. Some of these devices are temperature sensors, thermal and electrical conductivity devices, and liquid displacers. All such devices, however, require elimination of wave action against the device to obtain an accurate indication of the liquid level.
To prevent wave action from interfering with a liquid level indicating device, it has been common to put the device in a large diameter vertical pipe which communicates with the liquid and which extends from an anticipated low liquid level to a high liquid level. The pipe provides a stilling chamber containing the liquid in which the liquid level indicating device is essentially unaffected by wave or turbulent action.
The sight glass is a vertically extending tube preferably of a transparent material, such as glass provided with suitable gradations. The lower end of the tube is connected in communication with the liquid in the container so that the liquid level in the tube and the container will remain the same when the pressure, which may be atmospheric pressure, on the surface of the liquid and tube is the same. In such an arrangement, as liquid is removed from the container, the level of liquid in the tube follows the liquid level in the container thereby providing a continuous indication of the quantity of the liquid in the container. In certain circumstances, it is desirable to connect an alarm, or light, or other indicators to the sight glass so as to provide a remote means of determining when the liquid in the container has reached a high level or a low level condition. In certain circumstances, when the level of the liquid within the container is too high, it is important to be able to release liquid from the container so that an explosive condition is avoided. In other circumstances, when the low level is detected, it is important to add liquid to the container so as to avoid a “dry pumping” condition. In other circumstances, the use of the potentially empty container can result in an interruption in certain processes until additional liquid is added to the container.
Unfortunately, the use of a sight glass is often difficult where the liquid in the container has wave action or experiences turbulent conditions. As a result, the liquid in the sight glass will often bounce upwardly and downwardly. Any proximity switch that are used in association with the sight glass will experience a “bouncing” of the float therein. As a result, the alarm light or sound will become very intermittent as the float is in near proximity to the proximity switch. The bounce will cause the light to flicker on-and-off or the audible alarm to sound on-and-off. This often produces and erroneous indication to the person carrying out the monitoring. It is very difficult to know when the low level condition is actually achieved when the monitoring light is flickering on-and-off. As such, a need has developed so as to provide a positive indication when a low level or upper level condition has been reached.
In the past, various U.S. patents have issued relating to the detection of liquid levels in a container. For example, U.S. Pat. No. 3,942,379, issued on Mar. 9, 1976 to A. A. Kanzler, describes a floating wave stilling chamber for liquid level indicators. This device utilizes a gage mechanism that comprises a measuring means joined to a liquid level indicating device, and a floating stilling chamber circumscribing the periphery of the liquid level indicating device. The stilling chamber has a wall extending above the action of the wave action of the liquid. A vertical guide controls the lateral movement of the chamber at all levels in which the liquid level is to be measured.
U.S. Pat. No. 3,956,934, issued on May 18, 1976 to J. M. White, teaches a liquid level indicator for a pressurized liquid container. This indicator utilizes a gauge tube of transparent material having a check valve therein. The upper end of the gauge tube and the container communicating with the associated source of pressurized gas will normally maintain the check valve in the closed condition. The lower end of the gauge tube communicates with the dispensing conduit to thereby establish liquid communication between the container and the gauge tube so that the level of liquid in the gauge tube continuously corresponds to the level of liquid in the container while the check valve in the gauge tube maintains the liquid in the gauge tube during the dispensing of the liquid.
U.S. Pat. No. 4,048,856, issued on Sep. 20, 1977 to D. W. Conrad, describes a quick shut-off device with a direct reading liquid level indicator. This device attaches to the side of a liquid-filled container to measure the amount of liquid therein. Upper and lower valves have a sight glass extending therebetween. These valves are provided with ball valves to allow the on-off positions of the valves to be controlled by a 90° change in position of rods connected to the ball valves.
U.S. Pat. No. 4,155,013, issued on May 15, 1979 to J. Spiteri, teaches a liquid level indicator that utilizes the difference between the refraction of light by a prism in contact with air and by the same prism in contact with liquid being monitored so as to give a warning of low liquid level. Light is transmitted to a prism by an incoming fiberoptic lead and returned from the prism by a return fiberoptic lead.
U.S. Pat. No. 4,213,338, issued on Jul. 22, 1980 to A. L Hardy, also describes a liquid level indicator which provides a visual indication of the level within a rinse aid dispenser tank for dishwashers. This has a U-shaped tube containing an indicator liquid having one leg in communication with the lowermost region of the tank and with the other end disposed adjacent a viewing window. Air pressure generated in the connecting tubing by the relative liquid level in the tanks acts to control the position of the liquid in the U-shaped tube to provide a level indication at the viewing window.
U.S. Pat. No. 4,997,013, issued on Mar. 5, 1991 to A. E. Peckels, provides a liquid fill level indicator which has a non-electric fill indicator having an air passageway leading up and out of the vessel to an air flow indicator. The air escaping during filling causes the indicator to whistle. When the whistle stops, the vessel is filled and the user stops filling.
U.S. Pat. No. 5,103,674, issued on Apr. 14, 1992 to Outwater et al., describes a liquid level indicator for high-pressure, hostile environments. In particular, the hostile environment is a closed container of a nuclear reactor. This method provides a generally tubular structure connected to the closed container of the nuclear reactor so that the level of liquid in the tubular structure is indicative of the level of liquid in the closed container. A sealed buoyant float is sized to move vertically upwardly and downwardly within the tubular structure. The float is formed of beryllium. The location of float is detecting from outside the tubular structure. The vertical position of float corresponds to the level of liquid in the closed container.
U.S. Pat. No. 5,367,907, issued on Nov. 19, 1994 to S. Elfberson, also teach a liquid level indicator that comprises a rod of insulating material. The rod is a carrier for two parallel helically wound resistance wires and is surrounded by a float of insulating material displaceable along the rod by variations in the liquid level.
U.S. Pat. No. 5,900,546, issued on May 4, 1999 to L. C. Wilkins, describes a liquid level indicator for storage tanks. A float is slidable along the tube. The float is magnetically coupled to an ultrasound reflector piston inside the tube so that, when the tube is in the liquid in the tank, the float determines the height of the piston inside the tube. An ultrasonic transducer atop the tube sends pulses down the tube and which are reflected by the piston to the transducer. A computer coupled to the transducer determines and displays the liquid level.
U.S. Pat. No. 6,435,026, issued on Oct. 20, 2002 to W. L. Donehue, also provides a liquid level indicator. In this device, a magnetized float moves as the level of liquid changes. The indicator has a plurality of magnetized indicator elements disposed one above the other and past which the magnetized float travels as the liquid level rises or falls.
It is an object of the present invention to provide a liquid level indicator which provides a notice of when the level of liquid within a vessel has reached a low level or has reached a high level.
It is another object of the present invention to provide a system in which accounts for turbulent or wave action within the vessel.
It is a further object of the present invention to provide a system for a liquid level indication which effectively avoids false indications of low levels or high levels of the liquid within the vessel.
It is a further object of the present invention to provide a liquid level indicator system in which the sight glass will accommodate pressure releases.
It is a further object of the present invention to provide a liquid level indicator system which avoids problems associated with the “bounce” of the float.
It is still a further object of the present invention to provide a liquid level indicator system which easy to manufacture, relatively inexpensive, and easy to implement.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.